Video content transmitted over communication networks is generally subject to copyright. The copyright imposes strict legal limits on the ways in which subscribers are allowed to use the content that they receive from the network. For example, in addition to viewing video programs while they are broadcast, subscribers may be allowed to record the programs for their own use, but they are typically not permitted to distribute recorded copies of the programs. Notwithstanding these legal limitations, however, unauthorized copying and distribution of video content remains a major problem.
The following references are believed to represent the state of the art:    U.S. Pat. No. 7,738,673 to Reed; and    U.S. Pat. No. 8,027,509 to Reed, et al.